This proposal has as its goal a more complete specification of the information that serves to identify vowels in spoken syllables of American English (AE). Recent research has given strong support to the view that listeners use dynamic (time-varying) information available throughout the entire syllable to identify vowels. This research will investigate the locus and the interrelations of perceptually informative portions of the syllable, using the technique of electronic modification of natural speech stimuli. Modified stimuli are generated by altering, deleting and rearranging portions of the digitized waveforms of spoken syllables. The perceptual relevance of different combinations of these sources of information may be inferred from the perceptual error patterns in identification of the intended vowels by untrained listeners. Modifications include stimuli in which: 1) portions of syllables originally containing different initial and final consonants are recombined, 2) portions of syllables originally containing different vowels are recombined, and, finally, 3) portions of syllables produced by different speakers are recombined. In conjunction with these perceptual studies intensive acoustic analysis of the original stimulus materials will be pursued. By comparing the acoustic configurations of original syllables and electronically modified syllables which do and do not preserve vowel identity, the relational parameters that support vowel perception can be derived.